1. Field of the Invention
The present invention relates to circuitry adapted to be included in a satellite broadcast receiver.
2. Description of the Prior Art
Some satellite subscription television service systems scramble the video signals in a satellite broadcasting channel. The scrambled video signals cannot be displayed on the screen of the monitor unit of a satellite broadcast receiver if the scrambled video signals are fed directly to the monitor unit of the satellite broadcast receiver and, in general, aural (audio) signals are muted. The scrambled video signals received by the satellite broadcast receiver must be unscrambled by a scramble decoder to obtain unscrambled video signals, and then the unscrambled video signals (video signals and L-side aural signals and Reside aural signals) must be fed to the monitor unit. Thus, the satellite broadcast represented by scrambled video signals cannot be viewed and listened to by a satellite broadcast receiver not provided with any scramble decoder.
If a satellite broadcast is in a multivoice system, the viewer can optionally select the a main voice output mode, a subvoice output mode or a duplex voice output mode by operating a remote controller or a voice output mode selector key provided on the operating panel of the satellite broadcast receiver. For example, every time the voice output mode selector key is pressed, the main voice output mode, the subvoice output mode and the duplex voice output mode are selected sequentially and the selected voice output mode is displayed together with a channel number on the screen of the monitor unit as shown in FIG. 4.
The voice output mode of the received broadcast is identified by reading control bits (sixteen bits) subsequent to frame synchronizing signal bits in each frame of an aural signal as shown in FIG. 5. Usually, the first bit of the control bits is used for discriminating a transmission mode selected by a broadcast (an A mode or a B mode), the second and third bits identify the type of the aural signal (stereophonic aural signal, monophonic 2-channel aural signal (duplex voice system) or monophonic 1-channel aural signal) and the fourth and fifth bits identify the type of independent voice (stereophonic voice, monophonic 2-channel voice, monophonic 1-channel voice or a signal other than aural signals). The sixth bits and the following bits are used for extension.
Accordingly, the control unit of a BS tuner is able to identify the voice output mode of the received broadcast (an L+R mode, an L mode or an R mode for a stereophonic broadcast, or a main voice output mode, a subvoice output mode or a duplex voice output mode for a multivoice system) on the basis of the contents of voice identified by the control bit, and is able to execute switching control and display control.
A code representing a rule of compression and extension is written in range bits subsequent to the control bits in the aural signal construction shown in FIG. 5 and it is decided by reading the range bits if the received broadcast is scrambled.
Even if the video signal is scrambled so that the video signal cannot be displayed without unscrambling the scrambled video signal by a scramble decoder, the control bits, for instance, can be read out normally because only a voice data in the aural signal is scrambled. Accordingly, even if the scrambled broadcast has a plurality of voice output modes (a stereophonic broadcast or a multivoice broadcast), the broadcast can he neither viewed nor listened to because the satellite broadcast receiver is not provided with any scramble decoder and the voice output is muted, and the control unit controls the voice output mode on the basis of the data read from the control bits of the aural signal. That is, the voice output mode can optionally be selected by the viewer as stated above with reference to FIG. 4. However, the viewer is unable to discriminate the selected voice output mode.
For example, most satellite broadcast receivers have a last memory function for storing the last selected voice output mode, so that the subvoice output mode is selected in viewing a broadcast of a duplex voice output mode after the satellite broadcast receiver has been turned off after selecting the subvoice in the duplex voice output mode or when the channel is changed and a monaural broadcast is selected. If the voice output mode is changed without confirming the type of voice in receiving a scrambled broadcast by such a satellite broadcast receiver, it often occurs that a voice output mode not desired by the viewer is selected when a normal broadcast that is not scrambled is selected; consequently, the effect of the last memory function that enables the viewer to omit voice output mode selecting operation is nullified.